Known fuel cell stacks include a solid oxide fuel cell (hereinafter, may be referred to as an “SOFC”) stack which uses a solid electrolyte (solid oxide). The SOFC stack uses, as an electric power generating unit, for example, a fuel cell in which an anode and a cathode are provided on one side and the other side, respectively, of a solid electrolyte layer. In order to obtain desired electric power, a plurality of the fuel cells are arranged in series, thereby forming a fuel cell stack. Fuel gas and oxidizer gas to be used for generating electric power flow along the surfaces of anodes and cathodes, respectively, and fuel gas and oxidizer gas which have been used for generating electric power are discharged from the fuel cell stack.
There is disclosed a method for improving power generation efficiency through enhancement of overall fuel utilization rate by dividing the fuel cell stack into two blocks which differ in the number of fuel cells (refer to Patent Documents 1 and 2). Fuel gas is supplied sequentially to a block having a large number of fuel cells (upstream section) and then to a block having a small number of fuel cells (downstream section). Fuel gas which is not used for generating electric power in the upstream section is used in the downstream section, whereby overall fuel utilization rate is improved.